Not terribly bright by nature, Kastighurs typically serve more intelligent and more powerful demons. They work as hunters and jailers among the Tanar'ri, roles in which they take great pleasure. When a Tanar'ri need to find a creature but lacks the power to create a retriever, it calls upon a Kastighur or two to hunt the individual down.
A Kastighur's appetite for fear and the hunt sometimes gets the better of it - a fact that can frustrate it's master. A Kastighur sometimes intentionally allows one of the prisoners to escape, just so it can hunt down the fleeing creature. On a battlefield, a unit of Kastighurs breaks rank to chase enemies who seem frightened. Left to its own devices, a Kastighur roams the abyss hunting and killing whatever suits its fancy, whether a damned soul or even another Kastighur. It sees others of its kind as competition for attention of the great generals and demon lords who can take it to hunting grounds on other planes.
Thus Kastighurs despise one another unless they serve the same master. Even then, they view their service as a competition, and each always attempts to outdo the other in feats of combat. A Kastighur that has managed to survive, and thrive, for a long time might grow to gargantuan size. Such a fiend looks for opportunities to enslave and torture creatures of greater power, including dragons, powerful mortals, and other potent outsiders.